Demonstration of the SUS Calculator
Features & Benefits
 Score The SUS Properly: 10% of SUS questionnaires contain coding errors. The calculator includes several checks to prevent miscoding.
 Converts SUS scores to Percentile Ranks: Compare your SUS score to data from 500 studies by application type (e.g. websites, consumer software, hardware, IVRs). For example, a percentile rank of 75% tells you your application has higher perceived usability than 75% of all applications in the database.
 Converts SUS scores to Grades (A+ to F): Using my large database of studies, I converted the percentile ranks to letter grades. A grade of a "C" equals the 50th percentile (meaning average) and a grade of an "A" is any SUS score above an 80.3.
 Compares SUS Scores Statistically: Compare Two SUS scores, a single SUS score to a benchmark and generate confidence intervals. There are calculations for between and withinsubjects studies.
 Handles Missing Values: Uses a substitute method for estimating missing values which can be essential when sample sizes are small.
 Computes Sample Sizes: Instead of relying on general rulesofthumb, the calculator computes the best sample size for all studytypes.
 Checks for Inconsistent Respondents: The calculator flags respondents who are agreeing to too many favorable and unfavorable responses. This suggests users weren't paying attention or there was a coding error.
 Checks internal reliability: Cronbach's alpha is calculated from your raw responses. The calculator will tell you if the reliability of your responses is acceptable or poor.
Who Should BuyIf you use SUS, then you can benefit from this package. The 150 page guide is both a "howto" guide for those new to SUS and a reference for experienced researchers. The calculator reduces errors in coding and provides meaning to your SUS score by converting raw scores into percentile ranks and lettergrades. All the necessary statistical calculations from comparisons to sample size estimation are included.Guide Table of ContentsHighlights
The System Usability Scale
Background
SUS History & Development
Where did SUS come from?
How was SUS developed?
Scoring & Reporting SUS Scores
Scoring the SUS
Error Checks in the SUS Calculator
An Example Scored SUS Questionnaire
Should you report the mean or the median SUS Score?
What are possible SUS scores?
Handling missing values
Interpreting SUS Scores
Interpreting a SUS Score
SUS Grading on a Curve
Is a SUS score a percentage?
What is a good SUS score?
Can you report statistics on the individual items in the SUS?
Measuring changes in SUS over time
Properties and SUS Characteristics
Why are the items alternating between positive and negative wording?
Problems caused by alternating SUS items from positive to negative
Can SUS be used on websites?
Does SUS need to be administered during a usability test?
Does SUS provide an absolute measure of usability?
SUS Benchmark Data
SUS benchmarks by interface type
Summary Table of SUS Scores by Type of Interface
Definitions of benchmark sources
Source Table
Converting raw SUS score to percentile ranks
Modifying the SUS
Changing the wording of SUS items
Using an allpositively worded version of SUS
Adding items to SUS
Removing items from SUS
Changing the order of SUS Items
Changing the number of response options
Can I remove the neutral response?
SUS Reliability, Validity & Effectiveness
Does SUS have enough points of discrimination?
Are 10 items enough to measure usability?
How reliable is SUS?
How valid is SUS?
What other questionnaires are like SUS?
How SUS compares to other questionnaires
SUS & SUMI
SUS and WAMMI
Do SUS scores correlate with other usability metrics?
SUS and customer loyalty
Is SUS data normally distributed?
Detecting nonnormality
The central limit theorem
Robustness
Statements about the population
Normality summary
SUS is free: Do you get what you pay for?
Does SUS measure usability?
What else does SUS measure?
Is SUS reliable in different languages?
What factors affect the SUS scores?
Experience
Age
Gender
Education
Accounting for levels of experience when comparing products with SUS
Is SUS the best questionnaire to measure usability?
Common mistakes when using the SUS
Statistical Comparisons of SUS Scores
Confidence intervals around a SUS score
Comparing a SUS score to a benchmark
Assumptions
How do I generate a percentile score relative to a benchmark?
Determining whether SUS scores are significantly different
Withinsubjects comparison (paired ttest)
Confidence interval around the difference
Betweensubjects comparison (2sample ttest)
Why you don’t need to worry (too much) about violating assumptions
Sample Size
What is the minimum sample size needed?
Is a SUS score from a Small Sample Size Useless?
Standard deviation of the SUS
Calculating sample sizes for single SUS tests
Calculating sample sizes for comparing SUS scores
Betweensubjects
Withinsubjects
Calculating sample sizes for comparing a SUS score to a benchmark
Onesided confidence levels
Description of Data Sources
References
The System Usability Scale
All Positive Version of the System Usability Scale
About the Author
Select Sample Screen Shots
 Scoring, Reliability, Inconsistency Check & Missing Value Substitution
 Dashboard for Changes in SUS over time
 Converts SUS scores to Percentile Ranks & Grades
 Comparing Two SUS Scores (2sample ttest)
 Computing Sample Sizes
 All Positive SUS Scoring Sheet
 Sample Page 23
 Sample Page 24
 Sample page 65
 Sample Page 119
 The 150 Page Practical Guide to SUS
The guide provides stepbystep instructions for using the calculator as well as providing example calculations, benchmarks and the latest research on SUS from over 5000 responses. 
 Highlights
 Prevents Improper Coding
 Provides background and bestpractices and benchmarks
 Compares SUS Scores Statistically
 Handles Missing Values
 Computes Sample Sizes
 Checks for Inconsistent Respondents
 Converts SUS scores to Percentile Ranks
 Converts SUS scores to Grades (A+ to F)
 Discussion on SUS Reliability & Validity
 Understand what can and can't be modified on the SUS
 Checks Internal Reliability

What Customers are Saying:This is a great piece of work that will be useful to a lot of people.
John Brooke PhD System Usability Scale Creator The SUS calculator and the guide are terrific. I'm not a statistician so tools like this are a God send for me.
Randall Blair Usability Engineer Imodules Definitely a great toolkit for calculating the SUS. Well worth the purchase. And the best part, was the customer service!
Amy Coffey Business Consultant A model of lucidity and an indispensable handbook (in the true sense of
the word) for using the SUS questionnaire.
Jurek Kirakowski Ph.D. Human Factors Research Group, University College Cork, Ireland 